1. Technical Field
The present invention relates to a wireless communication apparatus and subcarrier allocation method, and particularly to a wireless communication apparatus and subcarrier allocation method where data is allocated to a plurality of subcarriers using, for example, OFDM.
2. Description of the Related Art
In the related art, multi-carrier transmission such as OFDM and MC-CDMA, etc., has been examined as a beyond 3G system taken as a system fulfilling high-speed packet transmission requirements. It is possible to improve frequency utilization efficiency in multi-carrier transmission by carrying out adaptive modulation and scheduling every subcarrier and by allocating data transmitted to each mobile station to subcarriers of superior reception quality within the communication band width using frequency scheduling. At base station apparatus, in order to carry out frequency scheduling by allocating data to be transmitted to each mobile station to subcarriers of superior reception quality, the mobile station notifies the base station apparatus of a CQI (Channel Quality Indicator) constituting individual channel quality information for every subcarrier for all subcarriers. The base station apparatus then determines the subcarrier, modulation scheme and coding rate to be used at each mobile station in accordance with a predetermined scheduling algorithm taking into consideration the CQI. Technology is disclosed, for example, in Japanese Patent Laid-open Publication No. 2002-252619 where frequency scheduling is carried out using all of the subcarrier CQI's from all of the users in the event that a base station transmits to a plurality of mobile stations at the same time.
Specifically, based on the CQI, the base station apparatus allocates a large number of subcarriers to each user in an appropriate manner (frequency division multiplexing) and selects an MCS (Modulation and Coding Scheme) for each subcarrier. Namely, based on channel quality, the base station apparatus satisfies the desired communication quality (for example, lowest transmission rate, lowest error rate) for each user, allocates subcarriers so as to achieve the maximum frequency utilization efficiency, and selects high-speed MCS for each subcarrier. This enables the implementation of a high throughput for a large number of users.
An MCS selection table decided in advance is used in the selection of MCS. The MCS selection table shows the correspondence between reception quality such as CIR (Carrier to Interference Ratio), etc., and error rates such as PER (Packet Error rate) or BER (Bit Error Rate), etc., for every MCS. During MCS selection, an MCS capable of satisfying the desired error rate is selected based on the measured reception quality.
FIG. 1 is a view showing the relationship between frequency and time in the case of allocating each item of data to a subcarrier block at the base station apparatus. From FIG. 1, the base station apparatus allocates all data to subcarrier blocks #10 to #14 using scheduling.
However, in the case of carrying out scheduling and adaptive modulation for every subcarrier block, it is necessary for communication terminal apparatus to report the CQI of every subcarrier to the base station apparatus. This means that the amount of control information sent from communication terminal apparatus to the base station apparatus is enormous and the transmission rate therefore falls. Further, it is also necessary for communication terminal apparatus to carry out processing to measure reception quality and generate the CQI, and for the base station apparatus to carry out processing for scheduling and adaptive modulation and suchlike for every subcarrier using the received CQI's. This means that the amount of signal processing occurring at the base station apparatus and communication terminal apparatus is extremely large, which makes it difficult to achieve lower power consumption and high signal processing speed.